The present invention relates to an assembly and to a method of installing a subsea structure on the seabed.
One envisaged field of application is in particular, but not exclusively, that of connecting subsea pipes on the seabed.
Systems for connecting two assemblies that can move with respect to each other are known. They generally require the intervention of a subsea robot or ROV (remotely operated vehicle), which includes its own propulsion means and is equipped with cameras, manipulators and a control system allowing an operator to remotely control it from the surface.
However, the seabed is very often covered with silt, sediment and various particles which are liable to produce clouds around the robot by said propulsion means, when the latter are directed toward the seabed. Such a cloud necessarily obscures the field view of the cameras and consequently the operator's visibility. This reduction in visibility impedes the progress of the connection operations and, sometimes, requires the intervention by the robot to be interrupted. Furthermore, the suspended particles may be deposited between the joints of the pipes to be connected, which is liable to impair the quality of the seal at the junction.
To reduce the visibility of clouds of particles appearing, it has been imagined to limit the tilt of the subsea robot. Thus, the propulsion means of said robot are not far from a horizontal direction approximately parallel to the seabed, thereby preventing layers of water lying close to the seabed from being moved and consequently generating clouds of particles. The reader may refer in particular to patent application FR 2 763 636 which describes such a device.
However, these devices designed to keep the subsea robot horizontal are relatively complex and limit the degrees of freedom of the robot.
Moreover, the height of the subsea structures above the seabed is generally considerable, so that the subsea robots operate some distance from the seabed and thus do not disturb the layers of water lying close to the seabed by the propulsion means.
However, such structures are necessarily bulkier and consequently require suitable installation means, which generally increases the installation costs.